Among other digital trinkets
Those who pre-order Company of Heroes 2 before the real-time strategy title launches this June will get a number of bonuses, including a Theatre of War mini-campaign. Seemingly unfinished right now, this extra spot of single-player content will arrive sometime after June 25.
What's more, Relic Entertainment is throwing in the Winter Ambush and Voronezh Front skin packs for vehicles in multiplayer plus two additional commanders, also usable in CoH 2 multiplayer. For the German army, we're looking at Joint Operation Doctrine (Precise artillery strike abilities) and Offensive Spearhead Doctrine (Heavy armor and airstrike abilities); for the Soviet army, it's Anti-Infantry Tactics Doctrine (Confers additional units such as the flamethrower tank) and Conscript Support Tactics Doctrine (Rapid reinforcement abilities).
Often times I can get away with avoiding pre-order stuff simply because it's multiplayer-centric and missing out on skins doesn't bother me. But single-player levels? That's a different story.